Glaciotectonic deformation within a flute from the Isfallsglaciären, Sweden

Abstract

The internal structure of a glacial flute in an area of fluted moraine outside the glacier Isfallsglaciären in the Kebnekaise massif, Lapland, northern Sweden, has been observed along a series of sections. The till in the flute is underlain by glaciofluvial or glaciolacustrine sediment that has been subject to extensive glaciotectonic deformation. The flute‐forming process is discussed and it is suggested that the flute was initiated beneath the warm‐based part of the glacier, by the sediment moving into the low pressure area in the lee side of a clast, associated with a deforming bed. It is suggested that deformation increased both down the lee and outwards from the centre line. These results were compared with fabric data from two other flute sites from Norway where similar deformation patterns were observed. It is suggested that because the deformation pattern in the flutes formed beneath both cold toe and warm based glaciers are similar, then the warm based deforming bed model is valid for both, followed by either passive freezing by the frozen toe moving over them or active freezing by the release of pressure from the surrounding ice, causing the water‐saturated till in the cavity to refreeze to the basal ice.

Evidence against pervasive bed deformation during the surge of an Icelandic glacier

“…Piotrowski & Kraus (1997) and Piotrowski & Tulaczyk (1999) show that the advance of the Weischelian ice sheet in Germany probably did not lead to pervasive deformation of the bed as had been previously inferred (e.g. Hart et al 1996), but resulted from enhanced basal sliding. Furthermore, Brown et al (1987) suggested that movement of the Puget lobe of the North American ice sheet was by sliding and localised deformation associated with ploughing.…”

“…The Quaternary ice sheets are also known to have advanced over large areas of soft sediment (e.g. Beget 1986;Hart et al 1996).…”

Formation and deformation of basal till during a glacier surge; Elisebreen, Svalbard

“…3 and 4). These are classical flutings formed by accumulation of subglacial sediments in the lee of lodged boulders (Paul and Evans, 1974;Boulton, 1976;Rose, 1989;Benn, 1994;Eklund and Hart, 1996;van der Meer, 1997b). F1 is 100 m long, up to 0.8 m high, and has a length/width ratio of ∼ 100:1 (Fig.…”

An assessment of fluting and “till esker” formation on the foreland of Sandfellsjökull, Iceland

“…Evidence for sediment deformation in flutings has been widely verified by clast macrofabrics (Boulton, 1976;Benn, 1994a;Eklund and Hart, 1996). The concept of converging "herringbone fabrics" is well established and demonstrates that particles on the flanks of flutings tend to be orientated obliquely downglacier toward the fluting axis, and additionally sediment deformation does not necessarily result in ice flow parallel A-axis clast alignments (Rose, 1989(Rose, , 1992Benn, 1994a).…”

“…Although several models of fluting formation exist, the most widely accepted model regards flutings as the product of subglacial sediment deformation in the lee of obstructions, such as large clasts, on the bed (Boulton, 1976;Benn, 1994a;Eklund and Hart, 1996). Flutings are initiated when weak, saturated sediment (till A horizon, Boulton and Hindmarsh, 1987) is squeezed or flows into small lee-side cavities behind obstructions, thereby filling up grooves on the underside of the glacier.…”